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BBC Micro Elite

Maths (Geometry): SPS3 (6502SP version)

Name: SPS3 [View in context] Type: Subroutine Category: Maths (Geometry) Summary: Copy a space coordinate from the K% block into K3
Copy one of the planet's coordinates into the corresponding location in the temporary variable K3. The high byte and absolute value of the sign byte are copied into the first two K3 bytes, and the sign of the sign byte is copied into the highest K3 byte. The comments below are written for the x-coordinate. Arguments: X Determines which coordinate to copy, and to where: * X = 0 copies (x_sign, x_hi) into K3(2 1 0) * X = 3 copies (y_sign, y_hi) into K3(5 4 3) * X = 6 copies (z_sign, z_hi) into K3(8 7 6)
.SPS3 LDA K%+1,X \ Copy x_hi into K3+X STA K3,X LDA K%+2,X \ Set A = Y = x_sign TAY AND #%01111111 \ Set K3+1 = |x_sign| STA K3+1,X TYA \ Set K3+2 = the sign of x_sign AND #%10000000 STA K3+2,X RTS \ Return from the subroutine